Hi ,
I have a spectrum analyzer HP8920a and during the self test RF DIAG I have the message "VCO 1Ghz Not locked". I checked at the board A15 and I have made some measurements. The output of the divider by 50 (signal 10_PLL10 pin 11 U10 and pin2 U27) is not working; there is no signal. At the entry of the divider by 50 the 500MHz?signal is correct.
The problem is the schematic in the user manual is different from the board. In the user manual the divider uses U27 MC1201 and U18 MC1038, and on the board there are U27 74AC191 and U18 "1820 8762".
I try to find some datasheet about this circuit 1820 8762 I don't find anything on the web. For the 74AC191 no problem; I have the datasheet.
To test the board I just put the power supply voltages +12V, -12V, +5V on the P2. In that manner it's possible to easily?test the board A15.
So my PLL is out of? lock because it's missing the signal "10_PLL10" pin 11 of U10. Has anyone ever encountered this problem? If someone has the datasheet of U18 "1820 8762" and the schematic of this divider by 50, it would be nice.
Thank you for your help.
F4EYM.
